Please stop, slow down, catch your breath and actually read what others have written.
Breath tests for alchol, test if you are under the influence, hence they are effective for their intended purpose - ensuring the safety of the public. Urine and blood tests do not test if you are under the influence, hence they are not effective for their intended purpose - ensuring the safety of the public.
Not exactly. Breath tests do NOT test whether you are "Under the Influence" of Alcohol, they merely test your current "Blood Alcohol Level" - which is related to being Under the Influence but specifically how much BAL it takes to actually be Under the Influence varies GREATLY from person to person. BAL is easy to test though and motor skill degradation isn't, since you don't have a baseline.
The current 0.08% Blood Alcohol Level that was politically pushed through under cover of darkness by MADD is Not Under the Influence for many people - though it may be for some people. There is unfortunately NO clear linkage between a specific BAL and UI, because there is so much variability in the population. Remember too that the previous BAL in most areas was 0.15%, and MADD's original founder left the organization she founded after this all happened because she felt they had become fanatical anti-alcohol whack-jobs with an agenda against alcohol rather than an agenda of improving safety.